Pre-synaptic kainate receptor-mediated facilitation of glutamate release involves PKA and Ca2+-calmodulin at thalamocortical synapses

Authors

  • Yuniesky Andrade-Talavera,

    1. Laboratorio de Neurociencia Celular y Plasticidad, Departamento de Fisiología, Anatomía y Biología Celular, Universidad Pablo de Olavide, Sevilla, Spain
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  • Paloma Duque-Feria,

    1. Laboratorio de Neurociencia Celular y Plasticidad, Departamento de Fisiología, Anatomía y Biología Celular, Universidad Pablo de Olavide, Sevilla, Spain
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  • Talvinder S. Sihra,

    Corresponding author
    • Department of Neuroscience of Physiology and Pharmacology, University College London, London, UK
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  • Antonio Rodríguez-Moreno

    Corresponding author
    • Laboratorio de Neurociencia Celular y Plasticidad, Departamento de Fisiología, Anatomía y Biología Celular, Universidad Pablo de Olavide, Sevilla, Spain
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Address correspondence and reprints requests to Dr Antonio Rodríguez-Moreno, Laboratory of Cellular Neuroscience and Plasticity, Department of Physiology, Anatomy and Cellular Biology, University Pablo de Olavide, Ctra. de Utrera, Km. 1, 41013, Sevilla, Spain. E-mail: arodmor@upo.es or Dr Talvinder S Sihra, Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK. E-mail: t.sihra@ucl.ac.uk

Abstract

We have investigated the mechanisms underlying the facilitatory modulation mediated by kainate receptor (KAR) activation in the cortex, using isolated nerve terminals (synaptosomes) and slice preparations. In cortical nerve terminals, kainate (KA, 100 μM) produced an increase in 4-aminopyridine (4-AP)-evoked glutamate release. In thalamocortical slices, KA (1 μM) produced an increase in the amplitude of evoked excitatory post-synaptic currents (eEPSCs) at synapses established between thalamic axon terminals from the ventrobasal nucleus onto stellate neurons of L4 of the somatosensory cortex. In both, synaptosomes and slices, the effect of KA was antagonized by 6-cyano-7-nitroquinoxaline-2,3-dione, and persisted after pre-treatment with a cocktail of antagonists of other receptors whose activation could potentially have produced facilitation of release indirectly. Mechanistically, the observed effects of KA appear to be congruent in synaptosomal and slice preparations. Thus, the facilitation by KA of synaptosomal glutamate release and thalamocortical synaptic transmission were suppressed by the inhibition of protein kinase A and occluded by the stimulation of adenylyl cyclase. Dissecting this G-protein-independent regulation further in thalamocortical slices, the KAR-mediated facilitation of synaptic transmission was found to be sensitive to the block of Ca2+ permeant KARs by philanthotoxin. Intriguingly, the synaptic facilitation was abrogated by depletion of intracellular Ca2+ stores by thapsigargin, or inhibition of Ca2+-induced Ca2+-release by ryanodine. Thus, the KA-mediated modulation was contingent on both Ca2+ entry through Ca2+-permeable KARs and liberation of intracellular Ca2+ stores. Finally, sensitivity to W-7 indicated that the increased cytosolic [Ca2+] underpinning KAR-mediated regulation of synaptic transmission at thalamocortical synapses, requires downstream activation of calmodulin. We conclude that neocortical pre-synaptic KARs mediate the facilitation of glutamate release and synaptic transmission by a Ca2+-calmodulin dependent activation of an adenylyl cyclase/cAMP/protein kinase A signalling cascade, independent of G-protein involvement.

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Ca2+/calmodulin involvement in pre-synaptic kainate receptors facilitation of glutamate release at thalamocortical synapses. We determined the mechanism by which kainate receptors (KARs) mediate a facilitation of glutamate release at thalamo-L4 cortical cell synapses. We find that an increase in cytosolic Ca2+ concentration, contingent on extra- and intra-cellular sources, in the pre-synaptic thalamic neuron, operates through the formation of Ca2+-calmodulin complexes to activate an AC/cAMP/PKA signalling pathway. This action of KARs may support learning and memory processes.

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